Oilfield operations (such as surveying, drilling, wireline testing, completions, production, and planning and oilfield analysis) are typically performed to locate and gather valuable downhole hydrocarbon fluids (such as oil and natural gas). Various aspects of the oilfield and its related operations are shown in FIGS. 1A-1D. As shown in FIG. 1A, surveys are often performed using acquisition methodologies, such as seismic scanners to generate maps of underground structures. These structures are often analyzed to determine the presence of subterranean hydrocarbon fluids. This information is used to assess the underground structures and locate the formations containing the desired subterranean hydrocarbon fluids. Data collected from the acquisition methodologies may be evaluated and analyzed to determine whether such hydrocarbon fluids are present, and if they are reasonably accessible.
As shown in FIGS. 1B-1D, one or more wellsites may be positioned along the underground structures to gather hydrocarbon fluids from the subterranean reservoirs. The wellsites are provided with tools capable of locating and removing hydrocarbon fluids from the subterranean reservoirs. As shown in FIG. 1B, drilling tools are typically advanced from rigs and into the earth along a given path to locate the downhole hydrocarbon fluids. During the drilling operation, the drilling tool may perform downhole measurements to investigate downhole conditions. In some cases, as shown in FIG. 1C, the drilling tool is removed and a wireline tool is deployed into the wellbore to perform additional downhole testing. After the drilling operation is complete, the well may then be prepared for production. As shown in FIG. 1D, wellbore completions equipment is deployed into the wellbore to complete the well in preparation for the production of fluid therethrough. Fluid is then drawn from downhole reservoirs, into the wellbore and flows to the surface. Facilities are positioned at surface locations to collect the hydrocarbons from the wellsite(s). Fluid drawn from the subterranean reservoir(s) passes to the facilities via transport mechanisms, such as tubing.
Production can involve enhanced recovery techniques and/or stimulation processes that are performed to enhance the productivity of a well. Enhanced oil recovery can begin at any time during the productive life of an oil reservoir. Its purpose is not only to restore formation pressure, but also to improve oil displacement or fluid flow in the reservoir. The four major types of enhanced oil recovery operations are water flooding, chemical flooding (e.g., alkaline flooding or micellar-polymer flooding), miscible displacement (e.g., carbon dioxide injection or hydrocarbon injection), and thermal recovery (e.g., steamflooding steam-assisted gravity drainage, or in-situ combustion). Stimulation processes generally fall into two main groups, hydraulic fracturing processes and matrix processes. Hydraulic fracturing processes are performed above the fracture pressure of the reservoir formation and create a highly conductive flow path between the reservoir and the wellbore. Matrix processes are performed below the reservoir fracture pressure and generally are designed to restore the natural permeability of the reservoir following damage to the near-wellbore area. Stimulation in shale gas and shale oil reservoirs typically takes the form of hydraulic fracturing processes. Various equipments may be positioned about the oilfield to monitor oilfield parameters and/or to manipulate the oilfield operations.
During the oilfield operations, data is typically collected for analysis and/or monitoring of the oilfield operations. Such data may include, for example, subterranean formation, equipment, historical and/or other data. Data concerning the subterranean formation is collected using a variety of sources. Such formation data may be static or dynamic. Static data relates to, for example, formation structure and geological stratigraphy that define the geological structure of the subterranean formation. Dynamic data relates to, for example, fluids flowing through the geologic structures of the subterranean formation over time. Such static and/or dynamic data may be collected to learn more about the formations and the valuable assets contained therein.
Sources used to collect static data may be seismic tools, such as a seismic truck that sends compression waves into the earth as shown in FIG. 1A. These waves are measured to characterize changes in the density of the geological structure at different depths. This information may be used to generate basic structural maps of the subterranean formation. Other static measurements may be gathered using core sampling and well logging techniques. Core samples may be used to take physical specimens of the formation at various depths as shown in FIG. 1B. Well logging typically involves deployment of a downhole tool into the wellbore to collect various downhole measurements, such as density, resistivity, etc., at various depths. Such well logging may be performed using, for example, the drilling tool of FIG. 1B and/or the wireline tool of FIG. 1C. Once the well is completed, fluid flows to the surface using tubing as shown in FIG. 1D. As fluid passes to the surface, various dynamic measurements, such as fluid flow rates, pressure, and composition may be monitored. These parameters may be used to determine various characteristics of the subterranean formation.
Sensors may be positioned about the oilfield to collect data relating to various oilfield operations. For example, sensors in the drilling equipment may monitor drilling conditions, sensors in the wellbore may monitor fluid composition, sensors located along the flow path may monitor flow rates, and sensors at the processing facility may monitor fluids collected. Other sensors may be provided to monitor downhole, surface, equipment or other conditions. The monitored data is often used to make decisions at various locations of the oilfield at various times. Data collected by these sensors may be further analyzed and processed. Data may be collected and used for current or future operations. When used for future operations at the same or other locations, such data may sometimes be referred to as historical data.
The processed data may be used to predict various aspects of the reservoir (such as downhole conditions of the reservoir) and make decisions concerning oilfield operations with respect to the reservoir. Such decisions may involve well planning, well targeting, well completions, operating levels, simulation rates and other operations and/or conditions. Often this information is used to determine when to drill new wells, re-complete existing wells, or alter wellbore production.
Data from one or more wellbores may be analyzed to plan or predict various outcomes at a given wellbore. In some cases, the data from neighboring wellbores or wellbores with similar conditions or equipment may be used to predict how a well will perform. There are typically a large number of variables and large quantities of data to consider in analyzing oilfield operations. It is, therefore, often useful to model the behavior of a reservoir and/or associated oilfield operations to determine the desired course of action. During the ongoing operations, the operating conditions may need adjustment as conditions change and new information is received.
Techniques have been developed to model the behavior of various aspects of a reservoir and associated oilfield operations, such as geological structures, downhole reservoirs, wellbores, surface facilities as well as other portions of the oilfield operation. Examples of these modeling techniques are shown in patent/Publication/application Nos. U.S. Pat. No. 5,992,519, WO2004/049216, WO1999/064896, WO2005/122001, U.S. Pat. No. 6,313,837, US2003/0216897, US2003/0132934, US2005/0149307, US2006/0197759, U.S. Pat. No. 6,980,940, US2004/0220846, and Ser. No. 10/586,283. Techniques have also been developed for performing reservoir simulation operations. See, for example, patent/Publication/application Nos. U.S. Pat. Nos. 6,230,101, 6,018,497, 6,078,869, GB2336008, U.S. Pat. No. 6,106,561, US2006/0184329, U.S. Pat. No. 7,164,990.
Despite the development and advancement of reservoir simulation techniques, there remains a need to consider the effects of uncertainty in computational models of reservoirs and associated oilfield operations.